The　infinite　domain　absorption　boundary　and　explosion　wave　input　method　are　two　keys　of　numerical　simulation　research　on　underwater　explosion.　This　paper　draws　on　the　seismic　wave　input　method　based　on　the　internal　substructure　and　the　multiscale　analysis　method　for　explosion　problems　based　on　the　substructure　of　explosion　source　and　proposes　a　shock　wave　input　method　for　underwater　explosion　based　on　the　substructure　of　explosion　source　considering　that　the　underwater　explosion　load　and　the　seismic　load　belong　to　the　same　fluctuation　problem.　The　method　first　decomposes　the　shock　wave　field　in　the　explosion　source　region　and　the　free　wave　field　motions　were　transformed　into　the　equivalent　explosive　loads,　which　enables　the　input　of　shock　waves　in　the　underwater　explosion　problem.　In　this　paper,　a　circular　substructure　of　explosion　source　is　used,　and　a　one-dimensional　model　in　AUTODYN　software　is　used　to　calculate　the　free　shock　wave　pressure　in　this　region　under　the　action　of　the　underwater　explosion.　Further,　based　on　the　continuous　fractional　approximation　method,　a　high-precision　time-domain　artificial　boundary　condition　is　proposed　to　simulate　the　radiation　effects　of　infinite　domain,　which　can　be　placed　close　to　the　structure　and　explosive　source　substructure　is　proposed.　The　method　proposed　in　this　paper　transforms　the　underwater　explosion　load　through　the　substructure　of　explosion　source　and　adopts　the　high　accuracy　absorption　boundary　to　greatly　reduce　the　calculation　area,　which　not　only　ensures　the　calculation　accuracy,　but　also　reduces　the　number　of　elements,　with　high　calculation　efficiency　and　practicability.　Finally　the　numerical　example　is　analyzed　to　verify　the　accuracy　of　the　model　and　method　of　this　paper,　The　pressure　time　history　curves　of　measuring　points　during　shock　wave　and　bubble　pulsation　stage　under　underwater　explosion　are　simulated,　and　the　effect　of　circular　structure　on　the　scattering　effect　of　underwater　near-field　explosion　wave　is　studied.　©　2023　Chinese　Journal　of　Theoretical　and　Applied　Mechanics　Press.　All　rights　reserved.